Hydraulically actuated synchronized transmission

ABSTRACT

A transmission shift system comprising a synchronizing device for idler wheels, which can be actuated hydraulically and comprises at least one piston that can mesh with a selected idler wheel as the sliding sleeve. The piston can be displaced axially on a shaft via a hydraulic actuation and is non-rotatably connected with it, thus self-locking synchronization is provided.

This application is a national stage completion of PCT/EP2003/006734filed Jun. 26, 2003 which claims priority from German Application SerialNo. 102 29 515.8 filed Jul. 2. 2002.

FIELD OF THE INVENTION

The present invention relates to a transmission shift system for idlerwheels.

BACKGROUND OF THE INVENTION

From the state of the art, transmission shift systems for idler wheelsare known. In the familiar transmission shift systems generallysynchronizing devices are provided for the purpose of synchronizing theidler wheels, wherein the devices actuate the sliding sleevesmechanically in order to synchronize the desired idler wheel with ashaft.

From the publication DE 43 24 814 A1, a transmission with a locksynchronization arrangement is known, wherein a synchronizer member thatis connected to a transmission shaft and at least one gear wheelrotating at a different speed can be positively coupled duringsynchronous speed with the help of an annular sliding sleeve that isaxially displaceable by the gearshift force. A synchronizer ring isprovided, between the sliding sleeve and each gear wheel, wherein partsof the synchronizer ring form a positively engaged coupling with partsof the gear wheels. In the absence of synchronization, the axialmovement of the sliding sleeve is blocked by blocking surfaces oflocking teeth. In such a transmission, the synchronization is alsoshifted mechanically via the sliding sleeve.

The publication DE 37 11 490 C2 discloses a gear shifting device. Inthis gear shifting device, the sliding sleeve is actuated by anadjusting arrangement accommodated in the shaft and operated by means ofhydraulic fluid, wherein the arrangement consists of a hydraulicallyactuatable piston arrangement. A connecting pin, which connects thesliding sleeve to the hydraulic piston arrangement, is provided, whichextends through a hole with axial play that is arranged transversely inthe shaft. The familiar gear shifting device disadvantageously requiresa very complex layout since the actuating device or piston arrangementis accommodated in the shaft. This affects the manufacturing costs ofthe familiar gear shifting devices negatively.

It is the object of the present invention to suggest a transmissionshift system of the aforementioned kind, which comprises a synchronizingdevice with a simple design and which additionally can be selected aseasily as possible.

SUMMARY OF THE INVENTION

A transmission shift system, according to the invention, is suggested inwhich the piston, which is provided as the sliding sleeve, is actuatedhydraulically, wherein a self-locking synchronizing device is provided.The piston is axially arranged, displaceable on a shaft by means ofhydraulic actuation and is connected with the shaft in a non-rotatablefashion. Furthermore, the piston is provided on the circumference of theshaft, resulting in a synchronizing device with axial friction surfaceson the idler wheel with a very simple design. Beneficially, only acertain hydraulic pressure level is required for actuation. The pressurelevel can, therefore, be selected via simple switching valves.

Within the framework of a further beneficial development of theinvention, it can be provided that the synchronizing device comprises atleast one piston that can mesh with a selected idler wheel. The pistonis, therefore, displaced axially on the shaft by means of hydraulicactuation. To return the piston to an idle position of the synchronizingdevice, at least one suitable return spring element or the like can beprovided.

The piston can preferably be designed as an annular flange that isstep-shaped in its cross-section, wherein it is seated in a pistoncarrier, which is firmly connected to the shaft. Between the piston andthe piston carrier, a piston chamber is provided for hydraulicactuation, which is preferably supplied with pressure oil. The piston,which is designed as an annular flange, can be equipped on its outerstep with first interior gear teeth as the coupling teeth to the idlerwheel and with second interior gear teeth on the inner step to connectto the shaft.

Pursuant to a further development of the present invention, the idlerwheel which is seated rotatably on the shaft and can comprise runninggears, which are positively connected to additional torque-transmittingelements. Furthermore, coupling teeth can be provided for positiveconnection with the piston on the idler wheel in the shifted-throughstate.

The idler wheel can preferably be seated on a profile element or thelike of the shaft. It is also conceivable for a rolling or plain bearingto be used to seat the idler wheel.

The piston carrier can alternatively also form a single component withthe shaft. To seal the piston chamber at least one sealing element canbe provided, which is preferably installed in a corresponding recess onthe piston carrier. It is also possible to arrange one or more sealingelements, such as sealing rings or the like, on the piston.

A further development of the present invention can provide that in theaxial direction between the piston and the idler wheel a first frictionplate with inside and outside teeth is arranged. The outside teeth arepreferably chamfered at least on the end facing the piston so that thefirst friction plate acts as a locking element during the synchronizingphase and represents a self-locking synchronizing device. Furthermore, asecond friction plate can be arranged on the side of the idler wheelthat faces away from the piston. It is especially beneficial if thefirst friction plate and the second friction plate are identical indesign so that the production requirements are reduced.

Alternatively a third friction plate, which forms an outside plate, anda fourth friction plate, which forms an inside plate, can be arranged onthe transmission shift system pursuant to the invention, wherein theinside plate can be arranged between the outside plate and the secondfriction plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a cut sectional partial view of the transmission shift systempursuant to the invention with synchronization in idle;

FIG. 2 is a diagrammatic view of the positions of the various gearwheels in relation to one another pursuant to FIG. 1;

FIG. 3 is a cut sectional partial view of the transmission shift systempursuant to the invention with synchronization in the locking orsynchronization position;

FIG. 4 is a diagrammatic view of the positions of the various gearwheels in relation to one another pursuant to FIG. 2;

FIG. 5 is a cut sectional partial view of the transmission shift systempursuant to the invention with synchronization in the shifted state;

FIG. 6 is a diagrammatic view of the positions of the various gearwheels in relation to one another pursuant to FIG. 5;

FIG. 7 is a cut sectional partial view of another embodiment of thetransmission shift system pursuant to the invention withsynchronization; and

FIG. 8 is a diagrammatic view of the positions of the various gearwheels in relation to one another pursuant to FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 through 6, a possible embodiment of the transmission shiftsystem with a synchronizing device, according to the invention, isillustrated.

The synchronizing device comprises a piston 1, which is designed as astep-shaped annular flange and comprises first interior teeth 12 as thecoupling teeth with an idler wheel 3 on its outside step and secondinterior teeth 13 on its inside step for the purpose of connecting witha shaft 9. The piston 1 is axially displaceable on the shaft and isconnected to it non-rotatably, wherein the piston that is designed as anannular flange is provided on the circumference of the shaft. The end ofthe first interior teeth of the piston 12 or of the sliding sleevefacing the idler wheel 3 is chamfered at least in part.

In the axial direction, a first friction plate 2 with interior teeth 17and exterior teeth 18 is arranged between the piston 1 and the idlerwheel 3, wherein the side facing the idler wheel 3 serves as a frictionsurface. During a synchronizing phase, the first friction plate 2 isalso used as a locking element resulting in a self-locking synchronizingdevice. The exterior teeth 18 of the friction plate 2 are chamfered onthe end facing the piston 1. In the radial direction, the friction plate2 can rotate in its interior teeth in relation to the shaft 9 around theintermediate space between two adjoining teeth of the first interiorteeth 12 of the piston 1. For this purpose, the interior teeth of thefriction plate 2 are arranged with play to the shaft 9, which isdesigned to be as large as the intermediate space between two adjoiningteeth of the first interior teeth 12 of the piston 1.

The idler wheel 3 comprises running gears 15 and coupling teeth 16 withchamfered teeth on the side facing the friction plate 2. In anon-shifted state, i.e. in idle, the idler wheel 3 can rotate freely onthe shaft 9. The idler wheel 3 is seated rotatably on a profile 20 ofthe shaft 9.

In the axial direction, a second friction plate 4 is provided behind theidler wheel 3, the plate 4 comprising only one set of interior teeth 17′toward the shaft 9. On the sides of the friction plates 2, 4 that faceaway from the idler wheel 3, safety rings 7, 8 are provided, whichsupport the friction plates 2, 4 in an axial direction. The frictionplates 2, 4 contain a suitable friction coating on the frictionsurfaces.

The piston 1 is seated in a piston carrier 5, which is firmly connectedto the shaft 9. The piston carrier 5 comprises a pressure oil feed line10 for hydraulically actuating the synchronizing device and suitablesealing elements 21, 21′ for sealing the piston chamber 1. Furthermore,return springs 6 are evenly distributed across the circumference of thepiston 1. The return springs 6 enable the piston 1 to return to itsposition in a non-shifted state.

FIG. 1 shows the transmission shift system in idle, according to theinvention. In idle, the piston 1 is held against a stop on the pistoncarrier 5 by the return springs 6. The piston chamber between the piston1 and the piston carrier 5 is without pressure in this state. The idlerwheel 3 can rotate freely on the shaft 9, wherein axial play exists,between the idler wheel 3 and the respective friction plates 2, 4. Withrespect to the circumferential direction, the first friction plate 2assumes any random position in its rotational play in relation to theshaft 9.

FIG. 2 illustrates that in idle, the chamfered teeth of the firstinterior teeth 12 of the piston 1 do not come into contact with thechamfered teeth of the exterior teeth 18 of the friction plate 2.

FIG. 3 shows a locking and synchronizing position of the transmissionshift system. The piston chamber between the piston 1 and the pistoncarrier 5 is fed with pressure oil in this position. Moving the piston 1eliminates the axial play between the idler wheel 3 and the respectivefriction plates 2, 4, and the friction plates 2, 4 are pushed againstthe safety rings 7, 8. Due to the friction torque acting in thecircumferential direction between the idler wheel 3 and the frictionplate 2, said plate is rotated against the piston 1 to its maximumrotational play. The chamfered teeth of the piston 1 rest against thechamfered teeth of the first friction plate 2, as illustrated in FIG. 4.In this locking and synchronizing position of the transmission shiftsystem, shifting of the piston 1 is prevented.

The circumferential force present on the friction plate 2 due to thefriction torque is greater than the circumferential force acting on thefriction plate 2 from the chamfered tooth surfaces of the piston 1. Thismeans that the piston 1 remains locked as long as a speed differential,and hence a corresponding friction torque, exists between the shaft 9and the idler wheel 3.

FIG. 5 shows the shifted state in which the idler wheel 3 is connectedpositively to the shaft 9 via the piston 1. As soon as the speeddifferential between the idler wheel 3 and the friction plate 2 movestoward zero, the circumferential force present on the first frictionplate 2 that is from this friction torque disappears. The piston 1 isthen able to rotate the friction plate 2 back so that the teeth of thefirst interior teeth 12 of the piston 1 can be guided through theintermediate spaces between the teeth of the exterior teeth 18 of thefirst friction plate 2, as is indicated in FIG. 6. The piston 1 canhence be shifted so that the piston 1 with the idler wheel 3 ispositively connected with the shaft 9.

To release the connection it is only necessary to eliminate the appliedpressure of the piston chamber between the piston 1 and the pistoncarrier 5. The return springs 6 then slide the piston 1 back into itsstarting position.

Should greater friction torque be required on the synchronizing device,another embodiment of the transmission shift system as illustrated inFIGS. 7 and 8 can be used.

The embodiment shown there represents a possible expansion of thepreviously illustrated embodiment. In this synchronizing device a thirdfriction plate 11 is provided as an exterior plate and a fourth frictionplate 19 is provided as an interior plate on the side of the idler wheel3 that faces away from the piston 1. The third friction plate 11 alsocontains interior teeth 17″ for the purpose of connection with the shaft9.

This way the number of friction surfaces can be increased to 4 in theembodiment illustrated here. The number of friction surfaces can befurther increased beyond the number shown here.

Reference numerals  1 piston  2 friction plate with interior andexterior teeth  3 idler wheel  4 friction plate with interior teeth  5piston carrier  6 return springs  7 safety ring  8 safety ring  9 shaft10 pressure oil supply line 11 third friction plate 12 first interiorteeth of the piston 13 second interior teeth of the piston 15 runninggears 16 coupling teeth of the idler wheel 17, 17′, 17″ interior teethon the friction plates 18 exterior teeth of the first friction plate 19fourth friction plate 20 profile 21, 21′ sealing rings/elements

1. A transmission shift system comprising a synchronizing device, for anidler wheel, which can be actuated hydraulically and comprises at leastone sliding sleeve piston (1) that can mesh with a selected idler wheel(3), the piston (1) is non-rotatably connected with a shaft (9) and canbe displaced axially on the shaft (9) by hydraulic actuation, aself-locking synchronization is provided by at least a first frictionplate (2, 4) comprising a friction surface facing the idler wheel (3);and at least the first friction plate (2, 4) comprises at least one setof interior teeth (17, 17′) which is provided for connection with theshaft (9).
 2. The transmission shift system according to claim 1,wherein the synchronizing device comprises a piston carrier (5)accommodating the piston (1), said piston carrier is non-rotatablyconnected to the shaft (9) and comprising a pressure oil feed line (10)so that a piston chamber, between the piston (1) and the piston carrier(5), is provided which can be supplied with pressure for hydraulicallyactuating the piston (1).
 3. The transmission shift system according toclaim 1, wherein the piston (1) is a step-shaped annular flange which,on an outside step, comprises first set of interior teeth (12) forconnecting with the idler wheel (3) and, on an inside step, comprisessecond set of interior teeth (13) for connecting with the shaft (9). 4.The transmission shift system according to claim 3, wherein at leastends of the first set of interior teeth (12) of the piston (1) facingthe idler wheel (3) are chamfered.
 5. The transmission shift systemaccording to claim 1, wherein the idler wheel (3) comprises a runninggear (15) for positive connection with an additional torque-transmittingelement and a set of coupling teeth (16) for positive connection withthe piston (1) and the idler wheel (3) is rotatably seated on the shaft(9).
 6. The transmission shift system according to claim 1, wherein inan axial direction between the piston (1) and the idler wheel (3), thefirst friction plate (2) with the set of interior teeth (17) and a setof exterior teeth (18) is provided, and the set of exterior teeth (18)is chamfered at least on an end facing the piston (1).
 7. Thetransmission shift system according to claim 1, wherein the firstfriction plate (2), during a synchronizing phase, is provided as alocking element resulting in a self-locking synchronizing device.
 8. Thetransmission shift system according to claim 1, wherein teeth of a firstset of interior teeth (12) of the piston (1) can be guided throughrespective intermediate spaces between teeth of a first set of exteriorteeth (18) of the first friction plate (2) for shifting purposes so thatthe piston (1), connected to the shaft (9), can be positively connectedto the idler wheel (3).
 9. The transmission shift system according toclaim 1, wherein a second friction plate (4) is arranged on a side ofthe idler wheel (3) facing away from the piston (1).
 10. Thetransmission shift system according to claim 9, wherein a third frictionplate (11) and a fourth friction plate (19) are provided, and the fourthfriction plate (19) is arranged between the second friction plate (4)and the third friction plate (11).
 11. The transmission shift systemaccording to claim 1, wherein at least one return spring (6) is providedfor returning the piston (1) to an unshifted position.
 12. Thetransmission shift system according to claim 11, wherein a plurality ofreturn springs (6) are provided, and the plurality of return springs (6)are evenly distributed about a circumference of the piston (1).
 13. Thetransmission shift system according to claim 1, wherein at least onesealing element (21, 21′) is provided between a piston carrier (5) andthe piston (1) to seal a piston chamber.
 14. The transmission shiftsystem according to claim 7, wherein interior teeth of the firstfriction plate (2) have play, in relation to the shaft (9), that is aslarge as an intermediate space between two adjoining teeth of a firstset of interior teeth (12) of the piston.